U.S. patent number 5,118,663 [Application Number 07/586,450] was granted by the patent office on 1992-06-02 for fabrication of silver coated high temperature ceramic superconductor fiber with metal substrate.
This patent grant is currently assigned to General Atomics. Invention is credited to Frederick H. Elsner, Michael V. Fisher, William A. Raggio, Lawrence D. Woolf.
United States Patent |
5,118,663 |
Woolf , et al. |
June 2, 1992 |
Fabrication of silver coated high temperature ceramic
superconductor fiber with metal substrate
Abstract
A method and apparatus for manufacturing a superconductor wire
has a wire take-up spool and a feed speed control spool. A wire
substrate is taken from the feed speed control spool and onto the
take-up spool as the wire take-up spool is rotated. The wire passes
through a container which holds a diffusion barrier material, where
the diffusion barrier material is electrophoretically deposited
onto the wire substrate and subsequently sintered. The wire is also
passed through a container which holds a superconductor material
suspended in solution, and a layer of the superconductor material
is electrophoretically deposited onto the diffusion barrier. The
grains of the superconductor layer are then magnetically aligned
and sintered. Also, a silver coating is electrophoretically
deposited onto the superconductor layer and sintered. A diffusion
bonding inhibitor material is then applied to the silver coating.
Then, the silver-coated superconductor wire is spooled and heated
to four hundred degrees centigrade (400.degree. C.) for (1) day to
oxidize the superconductor layer.
Inventors: |
Woolf; Lawrence D. (Carlsbad,
CA), Fisher; Michael V. (San Diego, CA), Raggio; William
A. (Del Mar, CA), Elsner; Frederick H. (Carlsbad,
CA) |
Assignee: |
General Atomics (San Diego,
CA)
|
Family
ID: |
24345779 |
Appl.
No.: |
07/586,450 |
Filed: |
September 21, 1990 |
Current U.S.
Class: |
505/232; 205/51;
419/20; 419/27; 419/7; 428/471; 428/632; 428/633; 505/211; 505/433;
505/434; 505/472; 505/739; 505/813; 505/821 |
Current CPC
Class: |
H01L
39/248 (20130101); Y10S 505/813 (20130101); Y10T
428/12618 (20150115); Y10S 505/739 (20130101); Y10T
428/12611 (20150115); Y10S 505/821 (20130101) |
Current International
Class: |
H01L
39/24 (20060101); H01B 012/00 () |
Field of
Search: |
;505/1,739,813,821
;419/7,20,27 ;428/632,633,471 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lechert, Jr.; Stephen J.
Attorney, Agent or Firm: Nydegger & Associates
Claims
We claim:
1. A method for manufacturing a high critical temperature
superconductor wire, which comprises the steps of:
extending a metallic wire substrate between a rotatable supply
spool and a rotatable take-up spool;
drawing said wire substrate from said supply spool to said take-up
spool through a processing zone with a predetermined tension on
said wire substrate;
fabricating said superconductor wire in said processing zone by
forming a ceramic superconductor layer on said metallic wire
substrate, said superconductor layer having a substantially uniform
thickness; forming a silver coating on said ceramic superconductor
layer; and depositing a ceramic powder on said silver coating;
and
rotating said take-up spool to wind said wire around said take-up
spool to form a coil of said wire.
2. A method as recited in claim 1 wherein said take-up spool is
continuously rotated to draw said wire around said take-up
spool.
3. A method as recited in claim 2 further comprising the step of
forming a diffusion barrier directly onto said metallic wire
substrate prior to forming said superconductor layer.
4. A method as recited in claim 3 wherein said diffusion barrier is
NdBa.sub.2 Cu.sub.3 O.sub.7-x, wherein O .ltoreq. x .ltoreq.
0.5.
5. A method as recited in claim 1 wherein said superconductor layer
is REBa.sub.2 Cu.sub.3 O.sub.7-x, (wherein O .ltoreq. x .ltoreq.
0.5) and RE is an element selected from the group consisting of
yttrium and elements having an atomic number between fifty-seven
(57) and seventy-one (71), inclusive, and combinations thereof.
6. A method as recited in claim 1 wherein said superconductor layer
forming step is accomplished by continuously drawing said wire
through a solution containing said superconductor, said solution
having an electrode disposed therein, said electrode having a
predetermined voltage established thereon with respect to said
metallic substrate, said superconductor layer being
eletrophoretically deposited onto said metallic wire substrate as
said substrate is drawn through said solution, said superconductor
layer being subsequently sintered.
7. A method as recited in claim 6 further comprising the steps of
determining the thickness of said superconductor layer, generating
a signal indicative of said thickness, and selectively varying said
predetermined voltage in response to said signal to vary the
thickness of said superconductor layer.
8. A method as recited in claim 1 wherein said silver coating step
is accomplished by continuously drawing said wire through a
solution containing said silver, said solution having an electrode
disposed therein, said electrode having a predetermined voltage
established thereon with respect to said metallic substrate, and
said silver coating being eletrophoretically deposited onto said
superconductor layer as said wire is drawn through said solution,
said silver coating being subsequently sintered.
9. A method as recited in claim 8 further comprising the step of
determining the thickness of said silver coating, generating a
signal indicative of said thickness, and selectively varying said
predetermined voltage in response to said signal to maintain the
thickness of said silver coating at a predetermined value.
10. A method as recited in claim 6 wherein said superconductor
layer is deposited onto said metallic wire substrate in grains, and
said method further comprises the step of magnetically aligning
said grains prior to said sintering step.
11. A method as recited in claim 1 wherein said ceramic powder is
yttrium oxide.
12. A method as recited in claim 1 wherein said take-up spool
containing said coil of said wire is heated in an oxygen containing
atmosphere for approximately one (1) day at approximately four
hundred (400.degree. C.).
13. A method for manufacturing a copper and oxygen containing
superconductor wire, which comprises the steps of:
continuously drawing a metallic wire substrate through a processing
zone at a predetermined tension;
positioning a first solution in said zone around said wire
substrate, said first solution containing ceramic superconductor
particles, said first solution having a first electrode disposed
therein;
selectively establishing a voltage on said first electrode with
respect to said metallic wire substrate to electrophoretically
deposit said superconductor particles onto said wire substrate;
sintering said superconductor particles;
positioning a second solution in said zone around said
superconductor grains, said second solution containing silver
particles, said second solution having a second electrode disposed
therein;
selectively establishing a voltage on said second electrode with
respect to said metallic wire substrate to electrophoretically
deposit said silver particles onto said superconductor grains to
form a silver coating thereon;
sintering said silver; and
covering said silver coating with a diffusion inhibiting layer.
14. A method as recited in claim 13 further comprising the step of
attaching said metallic wire substrate to a rotatable spool and
rotating said spool to accomplish said drawing step.
15. A method as recited in claim 14 wherein said superconductor
wire is drawn around said spool in a plurality of juxtaposed
coils.
16. A method as recited in claim 15 further comprising the step of
heating said coils at a predetermined temperature for a
predetermined time to establish a predetermined oxygen content in
said superconductor layer.
17. A method as recited in claim 13 further comprising the steps of
depositing a diffusion barrier onto said metallic wire substrate
and sintering said diffusion barrier prior to positioning said
first solution around said wire substrate.
18. A method as recited in claim 17 wherein said diffusion barrier
is NdBa.sub.2 Cu.sub.3 O.sub.7-x, (wherein O .ltoreq. x .ltoreq.
0.5).
19. A method as recited in claim 13 wherein said superconductor
layer is REBa.sub.2 Cu.sub.3 O.sub.7-x, (wherein O .ltoreq. x
.ltoreq. 0.5), and RE is an element selected from the group
consisting of yttrium and elements having an atomic number between
fifty-seven (57) and seventy-one (71), inclusive, and combinations
thereof.
20. A method as recited in claim 13 further comprising the step of
determining the thickness of said superconductor layer, generating
a signal indicative of said thickness, and selectively varying said
voltage on said first electrode in response to said signal to
maintain the thickness of said superconductor layer at a
predetermined value.
21. A method as recited in claim 13 further comprising the step of
determining the thickness of said silver coating, generating a
signal indicative of said thickness, and selectively varying said
voltage on said first electrode in response to said signal to
maintain the thickness of said silver at a predetermined value.
22. A method as recited in claim 13 further comprising the step of
magnetically aligning said superconductor particles.
23. A method as recited in claim 13 wherein said diffusion
inhibiting layer is yttrium oxide.
24. A ceramic superconductor wire formed by the process comprising
the steps of:
continuously drawing a wire substrate through a processing zone at
a predetermined tension;
positioning a first solution in said zone around said wire
substrate, said first solution containing ceramic superconductor
particles, said first solution having a first electrode disposed
therein;
selectively establishing a voltage on said first electrode with
respect to said wire substrate to electrophoretically deposit said
superconductor particles onto said wire substrate;
sintering said superconductor particles;
positioning a second solution in said zone around said
superconductor particles, said second solution containing silver
particles, said second solution having a second electrode disposed
therein;
selectively establishing a voltage on said second electrode with
respect to said wire substrate to electrophoretically deposit said
silver particles onto said sintered superconductor particles to
form a silver coating thereon;
sintering said silver; and
covering said silver coating with a diffusion inhibiting layer.
25. The superconductor wire of claim 24, wherein said
superconductor particles are substantially magnetically
aligned.
26. The superconductor wire of claim 25, further comprising a
diffusion barrier positioned between said wire substrate and said
superconductor layer.
27. The superconductor wire of claim 26, wherein said diffusion
barrier is NdBa.sub.2 Cu.sub.3 O.sub.7-x, (wherein O .ltoreq. x
.ltoreq. 0.5).
28. The superconductor wire of claim 24, wherein said
superconductor layer is REBa.sub.2 Cu.sub.3 O.sub.7-x, (wherein O
.ltoreq. x .ltoreq. 0.5) and RE is an element selected from the
group consisting of yttrium and elements having an atomic number
between fifty-seven (57) and seventy-one (71), inclusive, and
combinations thereof.
Description
FIELD OF THE INVENTION
The present invention relates generally to methods and apparatus
for manufacturing superconductor wire. More particularly, the
present invention relates to methods and apparatus for
manufacturing ceramic superconductor wires which have a
superconducting transition temperature above twenty (20) Kelvins.
The present invention particularly, though not exclusively, relates
to methods and apparatus for manufacturing and spooling relatively
long lengths of high critical temperature ceramic superconductor
wires.
BACKGROUND OF THE PRIOR ART
Recent advances in ceramic superconductor technology have made a
wide variety of superconductor applications technically possible
and economically feasible. This is because, as is well-known,
ceramic superconductors have relatively high superconducting
transition temperatures (T.sub.c), as compared to previously known
superconductors, e.g., niobium-based superconductors. As a
consequence of the high T.sub.c of modern ceramic superconductors,
relatively expensive and difficult to handle coolants such as
liquid helium, which had been required to cool previously known
superconductors to about four (4) Kelvins in order to achieve
superconductivity, are not required to cool modern ceramic
superconductors. Instead, modern ceramic superconductors can be
cooled to their superconducting state with relatively inexpensive
and easy to handle coolants, e.g., liquid nitrogen.
One obvious application of high-T.sub.c superconductors is the
transmission of electricity. Not surprisingly, several methods have
been developed for forming ceramic superconductors into electrical
transmission wires. Unfortunately, ceramic superconductors tend to
be brittle and easily broken, while electrical wires must typically
be flexible and relatively impervious to breaking under ordinary
operating conditions. Accordingly, methods for coating a flexible
metallic wire substrate with a ceramic superconductor layer have
been disclosed, e.g. the process disclosed in copending U.S. patent
application Ser. No. 265,827, entitled "Substrate for a Ceramic
Superconductor", assigned to the same assignee as the present
invention.
While supporting a ceramic superconductor layer on a substrate can
help alleviate the brittleness problem noted above, at least to
some extent, where the substrate is a flexible wire other technical
complications can arise. For example, material from the wire
substrate can diffuse into the ceramic crystal structure and dope
the crystal structure. This doping of the ceramic crystal structure
can limit the amount of current the superconductor layer can carry
in the superconducting state. Accordingly, processes such as the
method disclosed in co-pending U.S. patent application Ser. No.
528,707, entitled "Method for Electroplating of Yttrium Metal in
Nonaqueous Solutions", have been introduced which disclose methods
for forming a diffusion barrier between the substrate and
superconductor. Additionally, the ceramic superconductor must be
protected from water and other contaminates that could potentially
damage the ceramic or destroy the ceramic's superconducting
properties. Thus, it is desirable that the superconductor wire be
coated with a material which will have minimal chemical interaction
with the ceramic material, but which will provide a protective
cover with low electrical contact resistance for the ceramic
material. A method for coating a ceramic with a protective layer is
disclosed in a co-pending U.S. patent application entitled
"Anhydrous Electrophoretic Silver Coating Technique", assigned to
the same assignee as the present invention. Finally, ancillary
steps in the superconductor wire manufacturing process may be
desirable. For example, it may be desirable to magnetically align
the grains of the superconductor ceramic layer, in order to
maximize the current carrying capacity of the wire in its
superconductive state. Additionally, it may be desirable to provide
a diffusion inhibiting barrier to prevent the protective cover from
diffusing into exterior components during heating. Such a barrier
is disclosed in a co-pending U.S. patent application entitled "
Diffusion Bonding Inhibitor for Silver Coated Superconductor",
assigned to the same assignee as the present invention.
In light of the above discussion, it will be appreciated that the
manufacture of industrially useful ceramic superconductor wire can
involve several steps. In the case of a manufacturing process which
is designed to mass produce lengths of superconductor wire, the
steps discussed above are preferably accomplished in an integrated,
automated sequence, after which the manufactured superconductor
wire can be wound onto a spool or other industrially appropriate
configuration. The present invention recognizes that a ceramic
superconductor wire can be produced by a single apparatus using a
continuous, integrated process to fulfill each of the manufacturing
considerations noted above.
Accordingly, it is an object of the present invention to provide a
method and apparatus for manufacturing a ceramic superconductor
wire which produces an effectively flexible superconductor wire. It
is another object of the present invention to provide a method and
apparatus for manufacturing a ceramic superconductor wire with a
protective coating. A further object of the present invention is to
provide a method and apparatus for manufacturing a ceramic
superconductor wire in which the grains of the ceramic
superconductor are substantially aligned. Another object of the
present invention is to provide a method and apparatus for
manufacturing a ceramic superconductor wire in which a diffusion
barrier is established between the wire substrate and the ceramic
superconductor layer. Yet another object of the present invention
is to provide a method and apparatus for manufacturing a ceramic
superconductor wire which produces a superconductor wire in an
integrated, continuous process. Finally, it is an object of the
present invention to provide a method and apparatus for
manufacturing a ceramic superconductor wire which is comparatively
cost effective.
SUMMARY
An apparatus and method for manufacturing a ceramic superconductor
wire in accordance with the present invention includes a wire
take-up spool and a feed speed control spool. A metallic wire
substrate, preferably made of Duranickel 301, is attached to both
spools. The wire take-up spool is rotatable at a variable speed to
draw wire from the feed speed control spool, while the feed speed
control spool is also rotatable at a variable speed which is
operatively compatible with the speed of the take-up spool. A
tension sensor is positioned adjacent the wire between the spools
to sense the speed of the supply spool with respect to the take-up
spool and generate a control signal in response thereto. The signal
from the tension sensor is sent to a microprocessor or other
control unit, which controls the speed of rotation of the feed
speed control spool to establish the speed of the supply spool. A
minimum yet constant (and controllable) tension is provided by the
tension sensor.
As the wire substrate is drawn from the feed speed control spool to
the wire take-up spool, the wire substrate is passed through a
processing zone. As the wire is drawn through this processing zone,
it is covered or coated with successive layers of different
materials, which combine to form the final product. In radial order
from innermost layer to outermost layer, the layers of material for
the final product include a diffusion barrier, a superconductor
layer, a protective coating, and a diffusion inhibiting layer.
More specifically, the wire is drawn through a container which
holds a diffusion barrier material in solution with a solvent. As
intended for the present invention, this diffusion barrier material
is any suitable material which will substantially prevent diffusion
of materials from the wire substrate through the diffusion barrier
to the superconductor ceramic layer. In the preferred embodiment,
the diffusion barrier material is NdBa.sub.2 Cu.sub.3 O.sub.7-x,
the solvent is propylene carbonate and the material charging agent
is ethanolamine. In order to coat the substrate with the diffusion
barrier material, an electrophoresis process is used wherein the
substrate is established as an electrode. The other electrode of
this process is disposed in the solution, and a voltage is applied
to the electrodes to electrophoretically coat the metallic wire
substrate with a layer of the diffusion barrier material as the
wire substrate passes through the container. As the wire is drawn
out of the container, the wire is heated to evaporate solvents in
the diffusion barrier and the diameter of the wire is then measured
by an optical micrometer to determine the thickness of the
diffusion barrier. The micrometer then generates a signal which is
representative of the thickness of the diffusion barrier. This
signal is sent to a microprocessor, which selectively establishes
the voltage applied to the electrode in response to the signal from
the micrometer to control the thickness of the diffusion barrier.
The wire with diffusion barrier then passes through a furnace at
nine hundred degrees centigrade (900.degree. C.) in oxygen in order
to sinter the barrier layer material.
The wire substrate with diffusion barrier also passes through a
container which holds a ceramic superconductor material in
solution. In the preferred embodiment, the superconductor material
is DYBa.sub.2 Cu.sub.3 O.sub.7-x, and the solvent is propylene
carbonate and the material charging agent is ethanolamine. A layer
of this superconductor material is deposited onto the diffusion
barrier in the same manner in which the diffusion barrier was
deposited onto the wire substrate. More particularly, the substrate
is again used as an electrode and another electrode is positioned
in the superconductor solution. A voltage is then applied between
the electrodes to electrophoretically coat a layer of the
superconductor material onto the diffusion barrier as the wire
substrate passes through the container. As the wire is drawn out of
the container, the wire is heated to remove sufficient solvent from
the superconductor layer to increase the viscosity of the layer and
the diameter of the wire is measured by an optical micrometer to
determine the thickness of the superconductor layer. As before, the
micrometer generates a signal which is representative of the
thickness of the superconductor layer. This signal is sent to a
microprocessor, and the microprocessor establishes the voltage
applied to the electrode of the superconductor solution in response
to the micrometer signal to control the thickness of the
superconductor layer.
Importantly, the wire is also drawn past a permanent magnet to
magnetically align the crystal grains in the superconductor layer
which have been deposited over the diffusion barrier. In accordance
with the present invention, the magnetically aligned crystal grains
are sintered in an oxygen atmosphere at approximately one thousand
fifteen degrees centigrade (1015.degree. C.).
Continuing with the description of the processing of the wire, the
wire substrate with superconductor layer is also drawn through a
container which holds a nonaqueous alcohol-based silver slurry.
Again the substrate is used as an electrode and another electrode
is positioned in the silver slurry. When a voltage is established
between these electrodes, small particles of silver suspended in
the slurry are electrophoretically coated onto the superconductor
layer. Consequently, a protective coating of silver is formed over
the superconductor layer. An optical micrometer measures the
thickness of the silver layer as the wire passes out of the silver
slurry, and the voltage of the silver slurry electrode is
established by a microprocessor in response to the signal from the
optical micrometer. The silver coating is then sintered in an
oxygen atmosphere at approximately nine hundred degrees centigrade
(900.degree. C.).
Finally, a diffusion inhibiting powder is deposited onto the silver
coating by passing the wire through a solution containing ceramic
powder. In the preferred embodiment, the ceramic powder is yttria
or a rare earth oxide. The coated wire with yttria powder is then
wound around the wire take-up spool. To oxidize the superconductor
layer, the coils are removed from the coating apparatus and heated
in a separate furnace in the range of three hundred fifty to five
hundred degrees centigrade (350.degree. C.-500.degree. C.) for
approximately one (1) day. During this oxygenation process, the
yttria layer prevents the silver coatings of juxtaposed wires from
diffusing into each other during the oxidation process.
The novel features of this invention, as well as the invention
itself, both as to its structure and its operation, will be best
understood from the accompanying drawings, taken in conjunction
with the accompanying description, in which similar reference
characters refer to similar parts, and in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of the apparatus for manufacturing a
superconductor wire in accordance with the novel method of the
present invention;
FIG. 2 is a cross-sectional view of the superconductor wire
manufactured in accordance with the novel method of the present
invention, as would be seen along the line 2--2 in FIG. 1;
FIG. 3 is a perspective view of the superconductor wire
manufactured in accordance with the novel method of the present
invention, showing the wire in a spooled configuration, with
portions shown in phantom for clarity; and
FIG. 4 is a block diagram showing the steps of the novel method of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring initially to FIG. 1, an apparatus generally designated 10
is shown for manufacturing superconductor wire. As shown in FIG. 1,
apparatus 10 includes a rotatable feed speed control spool 12, a
rotatable wire supply spool 14, and a rotatable wire take-up spool
16. Spools 12 and 16 can be rotated at preselected speeds of
rotation by respective dc motors 18, 20, while supply spool 14 is
effectively freely rotatable on apparatus 10. A metallic wire
substrate 22 is attached to wire supply spool 14 and passes
partially around feed speed control spool 12, as shown. Wire
substrate 22 is also attached to wire take-up spool 16.
To transfer wire 22 from wire supply spool 14 to take-up spool 16,
motor 20 is energized to rotate wire take-up spool 16. Importantly,
a frictional rubber or plastic layer 24 is deposited onto the outer
circumference of feed speed control spool 12. Consequently, wire
substrate 22 cannot slide freely over the frictional layer 24 when
take-up spool 16 is rotated. Instead, to transfer wire past feed
speed control spool 12, feed speed control spool 12 must be
appropriately rotated to feed wire substrate 22 at a speed that is
compatible with the speed at which take-up spool 16 is able to
receive the substrate 22. The actual tension in wire substrate 22
as it passes from feed speed control spool 12 to take-up spool 16
is established by a tension sensor 26.
FIG. 1 further shows that a tension sensor 26 is positioned
adjacent wire substrate 22 for sensing the speed of the feed spool
with respect to the take-up spool and for generating a signal
representative of the differences of speed. Tension sensor 26 is
preferably a rotatable member which engages with substrate 22 and
which moves in response to changes in tension on the substrate 22.
Tension sensor 26 also includes appropriate electronic signal
processing components (not shown) which translate movement of the
rotatable arm into an output signal. As shown in schematic in FIG.
1, the output signal from sensor 26 is electrically conducted to a
microprocessor 27, which generates a control signal in response to
the speed of the feed spool. This control signal is sent to motor
18 to control the speed of rotation of feed speed control spool 12
(and, hence, to match the speed of the feed spool with the speed of
the take-up spool). establish a predetermined tension for wire
substrate 22). The details of the construction and operation of
tension sensor 26, microprocessor 27, and feed speed control spool
12 are disclosed in co-pending U.S. patent application entitled
"Wire Tension Control Apparatus", which is assigned to the same
assignee as the present invention.
Proceeding with the description of apparatus 10, FIG. 1 shows that
wire substrate 22 is drawn through a processing zone 28. In
accordance with the present invention, wire substrate 22 is
continuously drawn through zone 28 while wire substrate 22 is being
wound around take-up spool 16. Processing zone 28 includes a
diffusion barrier deposition region 30, a superconductor deposition
region 32, a protective coating deposition region 34, and a
diffusion inhibitor deposition region 35. Diffusion inhibitor
deposition region 35 may not be required, depending on the
requirements for the final product and on the desired reliability
of the coating system. Diffusion barrier deposition region 30
includes a container 36 which holds a solution 38 of diffusion
barrier material. Container 36 can be formed with a water tight
diaphragm 37 through which wire substrate 22 can be drawn. The
diffusion barrier material suspended in solution 38 is any
appropriate substance which can substantially prevent the diffusion
of material from substrate 22 to superconductor layer 70, shown in
FIG. 2, and which is chemically compatible with substrate 22 and
the superconductor material to be subsequently deposited onto
substrate 22. In the preferred embodiment, solution 38 is a mixture
of NdBa.sub.2 Cu.sub.3 O.sub.7-x particles with grain size of
one-tenth to ten (0.1-10) microns, (i.e., Neodymium-based 1-2-3
superconductor) where x is from zero to one-half (0-0.5),
inclusive, the solvent is anhydrous propylene carbonate, and the
particle charging agent is ethanolamine.
FIG. 1 shows that an annular electrode 40 is disposed in container
36 coaxially with container 36 to surround substrate 22. Electrode
40 is electrically connected to a voltage source 42, which is in
turn electrically connected to a microprocessor 44. Microprocessor
44 selectively causes voltage source 42 to establish a
predetermined voltage on electrode 40, to electrophoretically
deposit a layer of the diffusion barrier material that is contained
in solution 38 onto wire substrate 22. As shown in FIG. 1,
microprocessor 44 is electrically connected to a micrometer
controller 46, which receives the output signal of a non-contact
optical micrometer 48. Optical micrometer 48 is any suitable light
emitting diode (LED) device or laser device well-known in the
pertinent art which can measure the diameter of coated wire
substrate 22 and generate an output signal that is representative
of the thickness of diffusion barrier 50. This output signal is
transmitted through micrometer controller 46 to microprocessor 44.
Based upon the signal from micrometer controller 46, microprocessor
44 controls voltage source 42 to establish the predetermined
voltage on electrode 40, as described above. As is well-known in
the art, the voltage present on electrode 40 establishes the
thickness 90 of the diffusion barrier 50, shown in FIG. 2.
Referring back to FIG. 1, diffusion barrier deposition region 30 of
processing zone 28 is shown to further include a supply vat 52,
which contains a portion of solution 38. Diffusion barrier material
can be added to the portion of solution 38 which is held in vat 52
as required to maintain a predetermined concentration of the
diffusion barrier material in solution 38. Importantly, solution 38
can be circulated through lines 54, 56 from vat 52 to container 36
by a pump 58. Consequently, the solution 38 that is held in
container 36 can be replenished from vat 52.
To prevent the agglomeration of particulate material within vat 52,
an ultrasonic transducer 60 is positioned in vat 52 to
ultrasonically agitate solution 38. A suitable transducer power
supply 62 is electrically connected to transducer 60 to energize
transducer 60. Also, a magnetic stirrer 64 is positioned next to
vat 52 to magnetically agitate solution 38 using magnetic stir bar
39, to prevent sedimentation of the particles in solution 38.
FIG. 1 also shows that wire substrate 22 with diffusion barrier 50
is passed through an oven 66 that contains an inert atmosphere,
preferably argon or nitrogen gas, in which diffusion barrier 50 can
be heated to about two hundred degrees centigrade (200.degree. C.)
in order to evaporate the solvent portion of solution 38 that has
been electrophoretically coated onto substrate 22, leaving only the
barrier layer 50 particles attached to substrate 22. This
facilitates the measurement of the thickness 90 of diffusion
barrier 50 as described above.
As further shown in FIG. 1, wire substrate 22 with diffusion
barrier 50 is drawn through a furnace 68. Furnace 68 heats
diffusion barrier 50 to approximately nine hundred degrees
centigrade (900.degree. C.) in an oxygen atmosphere for
approximately one-tenth to two minutes (0.1-2 min.), to sinter
diffusion barrier 50, shown in FIG. 2. The barrier 50 needs to be
sintered at a sufficiently high temperature so that it will not
separate from substrate 22 when passing through subsequent inlet
diaphragm 37a, but not too high so as to minimize diffusion of
substrate 22 components into the diffusion barrier 50 grains or
particles.
Still referring to FIG. 1, superconductor deposition region 32 is
shown to include a container 36a which is formed with a leak-tight
diaphragm 37a. Container 36a is in all essential respects identical
in function and configuration to container 36. Container 36a holds
a suitable non-aqueous solvent in a solution 38a. A superconductor
material having the formula REBa.sub.2 Cu.sub.3 O.sub.7-x, where RE
is selected from the group consisting of yttrium and elements
having atomic numbers between fifty-seven (57) and seventy-one
(71), inclusive, and combinations thereof, and x is from zero to
one-half (0-0.5), inclusive, is dissolved in solution 36a. In the
preferred embodiment, the superconductor material is DyBa.sub.2
Cu.sub.3 O of particle size one-half to two (0.5-2) microns, the
solvent is anhydrous propylene carbonate and the material charging
agent is ethanolamine. FIG. 1 also shows that container 36a is
connected in fluid communication through lines 54a, 56a to a vat
52a. Pump 58a can circulate solution 38a from vat 52a to container
36a. FIG. 1 also shows that an ultrasonic transducer 60a is
positioned in vat 52a to ultrasonically agitate solution 38a. A
power supply 62a is electrically connected to transducer 60a to
energize transducer 60a. Also, a magnetic stirrer 64a is positioned
next to vat 52a to mechanically agitate the solution 38a using
magnetic stir bar 39a held within vat 52a.
An annular electrode 40a, similar in configuration and function to
electrode 40, is disposed in container 36a coaxially with container
36a. A voltage source 42a is electrically connected to electrode
40a to establish a voltage on electrode 40a relative to wire
substrate 22. Consequently, as wire substrate 22 with barrier 50 is
drawn through container 36a, the superconductor material suspended
in solution 38a is electrophoretically deposited onto diffusion
barrier 50 to form a superconductor layer 70, shown in FIG. 2.
Voltage source 42a is electrically connected to a microprocessor
44a, which is in turn electrically connected to a micrometer
controller 46a. Micrometer controller 46a is electrically connected
to an optical micrometer 48a, which sends a signal to micrometer
controller 46a that is representative of the thickness 96 of
superconductor layer 70, shown in FIG. 2. As was the case for
micrometer 48, micrometer 48a is any suitable non-contact optical
micrometer. Micrometer controller 46a sends the signal from
micrometer 48a to microprocessor 44a, which selectively controls
voltage source 42a to establish the voltage present on electrode
40a (and, hence, the thickness 96 of superconductor layer 70, shown
in FIG. 2).
FIG. 1 also shows that wire substrate 22 is passed through an oven
66a. Oven 66a heats superconductor layer 70 to approximately one
hundred degrees centigrade (100.degree. C.) in an inert gas
atmosphere (e.g., argon) to evaporate solvent from superconductor
layer 70. Importantly, after passing through oven 66a, some excess
solvent remains on superconductor layer 70 to establish a viscosity
of superconductor layer 70 which is appropriate for facilitating
the magnetic alignment of the superconductor grains which compose
layer 70.
More particularly, as shown in FIG. 1, wire substrate 22 with
superconductor layer 70 is drawn through permanent magnet 72.
Magnet 72 generates a magnetic field of approximately 1.5 tesla at
the wire position 73. This magnetic field at position 73 has a
direction which is appropriate for aligning the grains of
superconductor layer 70 for optimum current carrying capacity, in
accordance with well-known principles. As is well known in the art,
superconductor layer 70 can carry more current in the
superconductive state when the crystal grains of the superconductor
are magnetically aligned, as compared to a superconductor having
unaligned grains.
Continuing with the description of the apparatus 10 for
manufacturing superconductor wire in accordance with the present
invention, superconductor layer 70 is heated to approximately three
hundred fifty degrees centigrade (350.degree. C.) in an oven 74 to
completely bake off excess solvent from superconductor layer 70.
Layer 70 is heated to 350.degree. C. in oven 74 in an inert
atmosphere, preferably argon, in order to evaporate substantially
all remaining solvent from layer 70. As the skilled artisan will
appreciate, it is necessary to evaporate excess solvent from layer
70 because any remaining solvent would react with the oxygen in
furnace 68a to form CO.sub.2 which would deleteriously affect the
subsequent superconducting properties of superconductor layer 70.
Further, as shown in FIG. 1, wire substrate 22 with layer 70 is
drawn through furnace 68a to sinter superconductor layer 70. More
specifically, superconductor layer 70 is heated to approximately
one thousand fifteen degrees centigrade (1015.degree. C.) for two
to ten (2-10) minutes in an oxygen atmosphere inside furnace 68a to
sinter superconductor layer 70.
FIG. 1 also shows that wire substrate 22 with layer 70 is drawn
through silver coating deposition region 34. More specifically,
deposition region 34 is shown to include a container 36b which is
formed with a leak-tight diaphragm 37b. Container 36b is in all
essential respects identical in function and configuration to
container 36. Container 36b holds a suitable non-aqueous solvent in
a solution 38b. The solvent in solution 38b is preferably
non-aqueous in order to avoid adversely affecting the
superconducting properties of ceramic superconductor layer 70,
which, as is well known in the art, can be damaged by contact with
water. A silver coating will substantially prevent the diffusion of
water, carbon dioxide, and other undesired impurities into
temperature diffusion of oxygen through the silver to
superconductor layer 70, and will form a low electrical resistance
contact to the superconductor. In the preferred embodiment,
solution 38b includes silver particles of the type known in the art
as Metz Metallurgical silver powder type SED, of nominal particle
size of one-half to one and one-half (0.5-1.5) microns, and the
solvent is alcohol, preferably non-aqueous octanol. To establish a
means for the silver particles to carry a charge, a surfactant such
as oleic acid is deposited onto the silver particles before the
silver particles are placed in solution 38b: the type SED powder is
already of this form.
FIG. 1 also shows that container 36b is connected in fluid
communication through lines 54b, 56b to a vat 52b. Pump 58b can
circulate solution 38b from vat 52b to container 36b. Additionally,
FIG. 1 shows that a rotatable magnetic stirrer 64b is positioned
next to vat 52b to agitate the solution 38b using magnetic stir bar
39b held within vat 52b.
FIG. 1 further shows that an annular electrode 40b, which is
similar in function and configuration to electrode 40, is disposed
in container 36b concentrically with container 36b. A voltage
source 42b is electrically connected to electrode 40b to establish
a voltage on electrode 40b relative to wire substrate 22.
Consequently, as wire substrate 22 is drawn through container 36b,
the silver particles suspended in solution 38b are
electrophoretically deposited onto superconductor layer 70 to form
an electrically conductive protective coating 76, shown in FIG.
2.
FIG. 1 further shows that voltage source 42b is electrically
connected to a microprocessor 44b, which is in turn electrically
connected to a micrometer controller 46b. Micrometer controller 46b
is electrically connected to an optical micrometer 48b, which is a
laser or other suitable non-contact micrometer. Micrometer 48b
sends a signal that is representative of the thickness 104 of
protective layer 76, shown in FIG. 2, to micrometer controller 46b.
Micrometer controller 46b in turn sends the signal from micrometer
48b to microprocessor 44b, which selectively controls voltage
source 42b to establish the voltage present on electrode 40b (and,
hence, the thickness 104 of protective coating 76, shown in FIG.
2).
FIG. 1 also shows that wire substrate 22 is passed through an oven
66b. Oven 66b heats protective coating 76 to approximately two
hundred degrees centigrade (200.degree. C.) in an inert gas
atmosphere to evaporate excess solvent from protective coating 76,
to facilitate measuring the thickness of protective coating 76 by
optical micrometer 48b, as described above. FIG. 1 further shows
that wire 22 is drawn through a furnace 68b, where protective
coating 76 is sintered at approximately nine hundred degrees
centigrade (900.degree. C.) for approximately one-half to two
(0.5-2) minutes in an oxygen atmosphere.
Continuing with the description of apparatus 10, FIG. 1 shows that
wire substrate 22 with silver coating 76 is drawn through a
container 36c. Container 36c holds a non-aqueous solution 38c of a
ceramic powder (e.g., yttrium or rare earth oxide powder) in a
fluid medium such as isopropanol. As wire 22 is drawn through
container 36c, portions of the solution 38c adhere to silver
coating 76 to form diffusion inhibiting layer 78. FIG. 1 also shows
that container 36c is connected in fluid communication through
lines 54c, 56c to a vat 52c. A pump 58c can circulate solution 38c
from vat 52c to container 36c. Further, FIG. 1 shows that a
magnetic stirrer 64c is positioned next to vat 52c to magnetically
agitate the solution 38c held within vat 52c using a magnetic stir
bar 39c. If the liquid portion of solution 38c can evaporate at
room temperature, then only the ceramic powder will remain as
residue which forms a diffusion inhibiting layer 78 on the silver
coating layer 76. If the liquid portion of solution 38 does not
completely evaporate at room temperature, then the remaining
solution residue will evaporate or combust during the subsequent
heat processing steps disclosed below, leaving only the ceramic
powder residue on silver coating layer 76.
It is important that the diffusion inhibiting layer 78 will be
non-reactive with silver coating 76 during subsequent processing
steps. Specifically, it is important that layer 78 be non-reactive
with silver at the temperatures and during the time when the
superconductor layer 70 is being oxygenated. It has been determined
that a layer 78 of yttrium oxide (Y.sub.3 O.sub.2) ceramic powder
is effective for this purpose. Further, a stainless steel powder or
an aluminum powder could be effective.
Finally, FIG. 1 shows that wire substrate 22 is spooled onto wire
take-up spool 16. More particularly, as shown in FIG. 3, wire
substrate 22 is spooled onto take-up spool 16 in a plurality of
juxtaposed coils 80. Portions of each coil 80 may overlap and touch
portions of adjacent coils 80, as is common with spooled wires.
As shown in FIG. 3, after take-up spool 16 has received all of wire
substrate 27 which is to be processed, the spool 16 can be
positioned in a furnace 82 to oxidize superconductor layer 70. More
specifically, superconductor layer 70 is heated to three hundred
fifty to five hundred degrees centigrade (350.degree.
C.-500.degree. C.) in an oxygen atmosphere in furnace 82 for one
(1) hour to one (1) week, but preferably for approximately one (1)
day, to establish a predetermined oxygen content in superconductor
layer 70. Importantly, the respective protective coating 76 of each
coil 80 does not diffuse into juxtaposed coils 80 because such
diffusion is substantially prevented by respective diffusion
inhibiting layers 78. In addition, a metal spongy mesh material is
positioned between the spooled coils 80 and take-up spool 60 to
accommodate thermal expansion mismatch between spool 60 and coils
80 during oxygenation.
Referring back to FIG. 2, it is to be understood that wire
substrate 22 is made of a metallic substance, preferably Duranickel
301 or any of the materials listed in the table below:
TABLE 1 ______________________________________ COMPOSITION OF WIRE
SUBSTRATES (WEIGHT %) Ni Fe Cr Al Si Mn Mg Ti Zr B
______________________________________ Dura- 94.2 4.4 0.4 0.3 0.4
nickel 301 Hoskins- 71.5 22.5 5.5 0.5 875 Alumel 94.8 1.5 1.5 1.7
Inconel- 60 13 23 1.5 0.5 1.0 601 Haynes- 76.5 3 16 4.5 214 Nisil
95.5 4.4 0.1 Nicrosil 84.4 14.2 1.4 Ni.sub.3 Al 88.1 11.3 .6 .02
______________________________________
Alternatively, the following alloys may be used: Specifically,
these alloys include Ni.sub.1-x Al.sub.x (x .ltoreq. 0.25);
Ni.sub.x Al.sub.y B.sub.z (0.6 .ltoreq. x, 0.1 .ltoreq. y .ltoreq.
0.25, and z .ltoreq. 0.1); and Ni.sub.x Al.sub.y Cu.sub.z (0.6
.ltoreq. x, y .ltoreq. 0.25, and z .ltoreq. 0.25).
As disclosed above, diffusion barrier 50 is made of neodymium
"1-2-3" superconductor material. The neodymium 1-2-3 superconductor
is preferred for this purpose because it has a higher melting point
than the dysprosium 1-2-3 superconductor material which is used in
the 1-2-3 superconductor layer 70. Consequently, diffusion barrier
50 will not exhibit significant material diffusion/sintering when
the superconductor layer 70 is sintered, resulting in minimal
diffusion of substrate material into superconductor layer 70.
Finally, silver is the preferred material for protective coating
76, because silver establishes a water-impermeable protective
coating for superconductor layer 70, while permitting the diffusion
of oxygen through coating 76 to facilitate oxidation of
superconductor layer 70. Silver is also electrically conductive and
makes a low electrical contact resistance joint to superconductor
layer 70 when sintered at nine hundred degrees centigrade
(900.degree. C.). Consequently, silver coating 76 can provide an
electrical interconnection between superconductor layer 70 and
loads to which electricity is to be delivered.
METHOD OF MANUFACTURE
In the method of manufacturing a superconductor wire in accordance
with the present invention reference is made to FIGS. 1 and 4.
While the disclosure below sequentially describes the steps in
which the various barriers, layers, and coatings are deposited onto
substrate 22, it is to be understood that substrate 22 is
continuously drawn through processing zone 28 and that the steps
below are consequently performed simultaneously, but on different
portions, of substrate 22.
Wire substrate 22 is initially attached to wire supply spool 14 and
wire take-up spool 16. As shown in FIG. 1, substrate 12 is also
positioned against feed speed control spool 12. As indicated at
block 84 in FIG. 4, wire take-up spool 16 is rotated at a
predetermined speed to take up wire substrate 22 from wire supply
spool 14. As wire substrate 22 is consequently transferred from
supply spool 14 to take-up spool 16, a predetermined tension of
wire substrate 22 is established, as indicated at block 86. More
specifically, in accordance with previous disclosure, the speed of
rotation of motor 18 (and, hence, feed speed control spool 12) is
controlled by microprocessor 27 in response to the signal generated
by tension sensor 26 to establish the speed of the feed spool
14.
As wire substrate 22 is transferred from supply spool 14 to take-up
spool 16, wire substrate 22 passes through processing zone 28. As
indicated at block 88 in FIG. 4, diffusion barrier 50 is
electrophoretically deposited onto substrate 22 as substrate 22 is
drawn through container 36. More specifically, a voltage is
supplied from voltage source 42 to electrode 40 to cause the
NdBa.sub.2 Cu.sub.3 O.sub.7-x particles that are suspended in
solution 38 to be electrophoretically deposited onto substrate 22.
Microprocessor 44 controls voltage source 42 to control the voltage
present on electrode 40, and to thereby establish the thickness 90
of diffusion barrier 50. As disclosed above, microprocessor 44
controls voltage source 42 in response to the signal from optical
micrometer 48, which signal is representative of the thickness 90
of diffusion barrier 50. As shown in FIG. 1 and indicated at block
92 of FIG. 4, diffusion barrier 50 is sintered in furnace 68 at
approximately nine hundred degrees centigrade (900.degree. C.) for
approximately one-half to two (0.5-2) minutes.
In accordance with previous disclosure, substrate 22 with barrier
50 is also drawn through container 36a. As indicated at block 94 in
FIG. 4, superconductor layer 70 is electrophoretically deposited
onto barrier 50 when substrate 22 with barrier 50 is drawn through
container 36a. More particularly, in accordance with previous
disclosure, voltage source 42a provides a voltage for electrode
40a, which causes the DyBa.sub.2 Cu.sub.3 O.sub.7-x particles that
are suspended in solution 38a to be electrophoretically deposited
onto diffusion barrier 50. In response to the signal from optical
micrometer 48a, which is representative of the thickness 96 of
superconductor layer 70, microprocessor 44a controls voltage source
42a to control the voltage present on electrode 40a, and to thereby
establish the thickness 96 of superconductor layer 70.
Continuing with the description of the method of manufacture, the
individual grains of superconductor layer 70 are magnetically
aligned as substrate 22 with superconductor layer 70 is drawn past
magnet 72, as indicated at block 98 of FIG. 4. The aligned
superconductor grains of layer 70 are degrees centigrade
(1015.degree. C.) for approximately two to ten (2-10) minutes, as
indicated at block 100.
To coat superconductor layer 70 with a silver coating, substrate 22
with superconductor layer 70 is drawn through container 36b. As
indicated at block 102 in FIG. 4, silver coating 76 is
electrophoretically deposited over superconductor layer 70 as
substrate 22 is drawn through container 36b. More particularly,
voltage source 42b establishes a voltage on electrode 40b to cause
the surfactant-coated silver particles which are suspended in
solution 38b to be deposited onto superconductor layer 70. In
response to the signal from optical micrometer 48b, which is
representative of the thickness 104 of silver coating 76,
microprocessor 44b controls voltage source 42b. In turn, voltage
source 42b establishes the voltage present on electrode 40b, and
thereby establishes the thickness 104 of silver coating 76. As
indicated at block 106, silver coating 76 is sintered in furnace
68b at approximately nine hundred degrees centigrade (900.degree.
C.) for approximately one-half to two (0.5-2) minutes.
Block 108 indicates that a diffusion inhibiting layer 78 is
deposited over silver coating 76 as substrate 22 is drawn through
container 36c. More specifically, container 36c holds a non-aqueous
solution 38c in which a ceramic powder such as yttria powder is
dissolved. The yttria powder adheres to silver layer 76 to form
diffusion inhibitor layer 78 as substrate 22 is drawn through
solution 38c. Finally, some or all of the volatile parts of
solution 38c is evaporated from diffusion inhibitor layer 78 and
wire 22 is spooled onto wire take-up spool 16, as indicated at
block 110. As indicated at block 112 and shown in FIG. 3, spool 16
and substrate 22 can be heated in furnace 82 to a temperature of
about four hundred degrees centigrade (400.degree. C.) for a period
of between one (1) hour and one (1) week, and preferably for one
(1) day, to optimize the concentration of oxygen in superconductor
layer 70.
It will be appreciated by the skilled artisan that operation of the
apparatus of the present invention requires precise control over
several variables. Furthermore, the control of these variables will
be dependent on parameters of the system which are established to
be constant. With this in mind, the constant parameter of most
importance is the speed at which the wire substrate 22 is to be
drawn from supply spool 14 to take-up spool 16. Accordingly, given
that the wire substrate 22 is to be drawn from supply spool 14 to
the take-up spool 16 through the processing zone 28 at an
effectively constant speed, the time periods during which any
specific portion of the wire substrate 22 is subject to a
particular coating process or a particular heating process in the
processing zone 28 will be determined by the physical dimension of
the coating device or the heating device. This fact is most
important with regard to the heating devices. Specifically, and by
way of example, it is preferred that the oven 66 heat wire
substrate 22 for approximately one-tenth to two minutes. Thus,
depending on the speed at which the wire substrate 22 is drawn onto
take-up spool 16, and the exact time duration desired for the
heating process to be accomplished by oven 66, the dimensions of
the heating zone created by oven 66 can be determined. This same
rationale, of course, applies equally to all of the furnaces 66,
66a, 66b, 68, 68a, 68b and 74.
On the other hand, the coating devices are not as constrained by
dimensional limitations as are the heating devices. This is so due
to the fact that the thickness of the coatings deposited on the
wire substrate 22 at any particular stage in the fabrication
process will, for the most part, be determined by the voltage level
applied during the electrophoresis process and by the concentration
of powder particles in the slurries. Consequently, by establishing
dimensions for the furnaces 66, 66a, 66b, 68, 68a, 68b and 74 which
are compatible with the speed at which wire substrate 22 is drawn
through processing zone 28, and by varying the voltages applied by
the respective voltage sources 42, 42a and 42b as well as slurry
concentrations, the entire process of fabricating a superconductor
wire can be accomplished during the transfer of a wire substrate 22
from a supply spool 14 to a take-up spool 16.
While the particular process and apparatus for fabrication of
silver coated high temperature ceramic superconductor fiber with
metal substrate as herein shown and disclosed in detail is fully
capable of obtaining the objects and providing the advantages
herein before stated, it is to be understood that it is merely
illustrative of the presently preferred embodiments of the
invention and that no limitations are intended to the details of
construction or design herein shown other than as described in the
appended claims.
* * * * *